'First we will lose oxygen, then most of our surface water': Supercomputer predicts when life on Earth could end, says it is 'inevitable'

The end of life on Earth has long been a subject of speculation, from fictional doomsday scenarios to scientific predictions about the planet's distant future. One such prediction came in 2021 when scientists using supercomputer predicted a timeline when Earth's atmosphere could become too hostile to support complex life.

According to research published in Nature in 2021 by scientists Kazumi Ozaki and Christopher T. Reinhard, Earth's oxygen-rich atmosphere could survive for roughly another 1.08 billion years.

The researchers used a stochastic model to examine the long-term future of Earth's atmosphere and its ability to support oxygen-dependent life.


"Earth's modern atmosphere is highly oxygenated and is a remotely detectable signal of its surface biosphere. However, the lifespan of oxygen-based biosignatures in Earth's atmosphere remains uncertain, particularly for the distant future," Ozaki and Reinhard wrote in their study.

Using their model, the scientists estimated that the mean future lifespan of Earth's atmosphere with oxygen levels above 1% of today's atmospheric level is approximately 1.08 ± 0.14 billion years.

That means the timeline sometimes reported as the year 1,000,002,021 is not a precise date on which all life on Earth will suddenly disappear. Rather, it is an approximate extrapolation based on the study's estimate of when Earth's atmosphere could undergo major deoxygenation.

What happens to Earth's atmosphere?

The model suggests that Earth's atmosphere will eventually lose much of its oxygen, with atmospheric O2 levels falling sharply toward conditions resembling those of the ancient Archaean Earth.

Importantly, the researchers found that this atmospheric deoxygenation is likely to happen before Earth enters a moist greenhouse state and before the planet loses most of its surface water.

"We find that future deoxygenation is an inevitable consequence of increasing solar fluxes," the researchers wrote.

As the Sun gradually becomes brighter, Earth's climate and carbon cycle will change. The study suggests that these changes could eventually produce a carbon dioxide-limited biosphere followed by rapid atmospheric deoxygenation.

Such conditions would be devastating for oxygen-dependent organisms, including humans and many other complex forms of life.

The researchers, whose work involved scientists from Japan's Toho University and NASA-linked research, noted that an oxygen-rich atmosphere is not necessarily a permanent feature of a habitable planet.

Their findings also have implications beyond Earth's future. The researchers argued that scientists searching for life on planets outside our Solar System should not assume that an oxygen-rich atmosphere is the only possible indicator of life.

Another study predicts a different threat

Long before Earth's atmosphere becomes severely depleted of oxygen, another major threat could emerge.

Scientists at the University of Bristol have used computer modelling to examine what Earth could look like millions of years in the future as the continents gradually move toward one another.

Their research suggests that the continents could eventually merge into a new supercontinent called Pangea Ultima.

The resulting planet could be significantly hotter and drier, with increased volcanic activity and large areas becoming unsuitable for mammals.

Dr Alexander Farnsworth, the study's lead author and senior research associate at the University of Bristol, described the future supercontinent as a "triple whammy" caused by the continentality effect, a hotter Sun and increased carbon dioxide levels.

"The result is a mostly hostile environment devoid of food and water sources for mammals," Farnsworth said.

The study suggested that widespread temperatures could reach between 40 and 50 degrees Celsius (104 to 122 degrees Fahrenheit), with even higher daily extremes in some regions. Combined with high humidity, such conditions could make it extremely difficult for humans and other mammals to cool their bodies.